I just "100% completed" the singleplayer game, and the collection was, indeed, f00king tedious. I had thought there was a "you did it all!" Achievement, but there was not. Now I'll be clearing out the Activities and Story Missions in co-op mode. 85+ hours... And only a few of them felt like a grind: I'm looking at you, possibly-missed Stunt Jumps and item collection!
In contrast, I've gone back and fired up GTA IV a couple times, and while it is prettier and more atmospheric than SR2, and the writing for the radio shows is better at creating an immersive world, in all other ways SR2 is the better game. I've been playing a little The Lost and the Damned, and tried a little more vanilla GTA IV multiplayer, and it just... all that extra natural motion middleware and representational car handling -- it doesn't make the game more fun. It makes the game less responsive.
Why is it that, with all the effort Volition put into this excellent game, with ways of bringing the core game modes into the multiplayer experience with the Strong Arm mode, but whenever I join an MP game it's freakin' deathmatch free-for-all. Lame!